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TOI-1634 b: An Ultra-short-period Keystone Planet Sitting inside the M-dwarf Radius Valley

Cloutier, Ryan and Charbonneau, David and Stassun, Keivan G. and Murgas, Felipe and Mortier, Annelies and Massey, Robert and Lissauer, Jack J. and Latham, David W. and Irwin, Jonathan and Haywood, Raphaëlle D. and Guerra, Pere and Girardin, Eric and Giacalone, Steven A. and Bosch-Cabot, Pau and Bieryla, Allyson and Winn, Joshua and Watson, Christopher A. and Vanderspek, Roland and Udry, Stéphane and Tamura, Motohide and Sozzetti, Alessandro and Shporer, Avi and Ségransan, Damien and Seager, Sara and Savel, Arjun B. and Sasselov, Dimitar and Rose, Mark and Ricker, George and Rice, Ken and Quintana, Elisa V. and Quinn, Samuel N. and Piotto, Giampaolo and Phillips, David and Pepe, Francesco and Pedani, Marco and Parviainen, Hannu and Palle, Enric and Narita, Norio and Molinari, Emilio and Micela, Giuseppina and McDermott, Scott and Mayor, Michel and Matson, Rachel A. and Martinez Fiorenzano, Aldo F. and Lovis, Christophe and López-Morales, Mercedes and Kusakabe, Nobuhiko and Jensen, Eric L. N. and Jenkins, Jon M. and Huang, Chelsea X. and Howell, Steve B. and Harutyunyan, Avet and Fűrész, Gábor and Fukui, Akihiko and Esquerdo, Gilbert A. and Esparza-Borges, Emma and Dumusque, Xavier and Dressing, Courtney D. and Di Fabrizio, Luca and Collins, Karen A. and Cameron, Andrew Collier and Christiansen, Jessie L. and Cecconi, Massimo and Buchhave, Lars A. and Boschin, Walter and Andreuzzi, Gloria (2021) TOI-1634 b: An Ultra-short-period Keystone Planet Sitting inside the M-dwarf Radius Valley. Astronomical Journal, 162 (2). Art. No. 79. ISSN 0004-6256. doi:10.3847/1538-3881/ac0157.

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Studies of close-in planets orbiting M dwarfs have suggested that the M-dwarf radius valley may be well explained by distinct formation timescales between enveloped terrestrials and rocky planets that form at late times in a gas-depleted environment. This scenario is at odds with the picture that close-in rocky planets form with a primordial gaseous envelope that is subsequently stripped away by some thermally driven mass-loss process. These two physical scenarios make unique predictions of the rocky/enveloped transition's dependence on orbital separation such that studying the compositions of planets within the M-dwarf radius valley may be able to establish the dominant physics. Here, we present the discovery of one such keystone planet: the ultra-short-period planet TOI-1634 b (P = 0.989 days, F = 121 F_⊙, r_p = 1.790_(-0.081)^(+0.080) R_⊕) orbiting a nearby M2 dwarf (K_s = 8.7, R_s = 0.450 R_⊙, M_s = 0.502 M_⊙) and whose size and orbital period sit within the M-dwarf radius valley. We confirm the TESS-discovered planet candidate using extensive ground-based follow-up campaigns, including a set of 32 precise radial velocity measurements from HARPS-N. We measure a planetary mass of 4.91_(-0.70)^(+0.68) M_⊕, which makes TOI-1634 b inconsistent with an Earth-like composition at 5.9σ and thus requires either an extended gaseous envelope, a large volatile-rich layer, or a rocky composition that is not dominated by iron and silicates to explain its mass and radius. The discovery that the bulk composition of TOI-1634 b is inconsistent with that of Earth supports the gas-depleted formation mechanism to explain the emergence of the radius valley around M dwarfs with M_s ≾ 0.5 M_⊙.

Item Type:Article
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URLURL TypeDescription Paper
Cloutier, Ryan0000-0001-5383-9393
Charbonneau, David0000-0002-9003-484X
Stassun, Keivan G.0000-0002-3481-9052
Murgas, Felipe0000-0001-9087-1245
Mortier, Annelies0000-0001-7254-4363
Massey, Robert0000-0001-8879-7138
Lissauer, Jack J.0000-0001-6513-1659
Latham, David W.0000-0001-9911-7388
Haywood, Raphaëlle D.0000-0001-9140-3574
Guerra, Pere0000-0002-4308-2339
Giacalone, Steven A.0000-0002-8965-3969
Bieryla, Allyson0000-0001-6637-5401
Winn, Joshua0000-0002-4265-047X
Watson, Christopher A.0000-0002-9718-3266
Vanderspek, Roland0000-0001-6763-6562
Udry, Stéphane0000-0001-7576-6236
Tamura, Motohide0000-0002-6510-0681
Sozzetti, Alessandro0000-0002-7504-365X
Shporer, Avi0000-0002-1836-3120
Ségransan, Damien0000-0003-2355-8034
Seager, Sara0000-0002-6892-6948
Savel, Arjun B.0000-0002-2454-768X
Sasselov, Dimitar0000-0001-7014-1771
Rose, Mark0000-0003-4724-745X
Ricker, George0000-0003-2058-6662
Rice, Ken0000-0002-6379-9185
Quintana, Elisa V.0000-0003-1309-2904
Quinn, Samuel N.0000-0002-8964-8377
Piotto, Giampaolo0000-0002-9937-6387
Phillips, David0000-0001-5132-1339
Pedani, Marco0000-0002-5752-6260
Parviainen, Hannu0000-0001-5519-1391
Palle, Enric0000-0003-0987-1593
Narita, Norio0000-0001-8511-2981
Molinari, Emilio0000-0002-1742-7735
Micela, Giuseppina0000-0002-9900-4751
Mayor, Michel0000-0002-9352-5935
Matson, Rachel A.0000-0001-7233-7508
López-Morales, Mercedes0000-0003-3204-8183
Kusakabe, Nobuhiko0000-0001-9194-1268
Jensen, Eric L. N.0000-0002-4625-7333
Jenkins, Jon M.0000-0002-4715-9460
Huang, Chelsea X.0000-0003-0918-7484
Howell, Steve B.0000-0002-2532-2853
Fukui, Akihiko0000-0002-4909-5763
Esquerdo, Gilbert A.0000-0002-9789-5474
Esparza-Borges, Emma0000-0002-2341-3233
Dumusque, Xavier0000-0002-9332-2011
Dressing, Courtney D.0000-0001-8189-0233
Collins, Karen A.0000-0001-6588-9574
Cameron, Andrew Collier0000-0002-8863-7828
Christiansen, Jessie L.0000-0002-8035-4778
Buchhave, Lars A.0000-0003-1605-5666
Boschin, Walter0000-0001-9978-9109
Additional Information:© 2021. The American Astronomical Society. Received 2021 March 19; revised 2021 April 30; accepted 2021 May 13; published 2021 July 30. R.C. is supported by a grant from the National Aeronautics and Space Administration in support of the TESS science mission. C.D.D. acknowledges support from the Hellman Fellows Fund, the Alfred P. Sloan Foundation, the David & Lucile Packard Foundation, and the NASA Exoplanets Research Program (XRP) through grant 80NSSC20K0250. This work is made possible by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This material is based on work supported by the National Aeronautics and Space Administration under grant No. 80NSSC18K0476 issued through the XRP Program. The financial support from the agreement ASI-INAF n.2018-16-HH.0 is gratefully acknowledged. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated by the Fundación Galileo Galilei (FGG) of the Istituto Nazionale di Astrofisica (INAF) at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain). The HARPS-N project has been funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origins of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), the University of St Andrews, Queens University Belfast, and the University of Edinburgh. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP). MSIP is funded by NSF. This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos Sánchez operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. This work is partly supported by JSPS KAKENHI grant numbers JP18H01265 and JP18H05439, and JST PRESTO grant No. JPMJPR1775, and a University Research Support Grant from the National Astronomical Observatory of Japan (NAOJ). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. Some of the Observations in the paper made use of the High-Resolution Imaging instrument 'Alopeke. 'Alopeke was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. 'Alopeke was mounted on the Gemini North telescope of the international Gemini Observatory, a program of NSF's OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). Facilities: TESS - , ASAS-SN - , TRES - , LCOGT - , MuSCAT2 - , OAA - , RCO - , Gemini/'Alopeke - , Lick/ShARCS - , TNG/HARPS-N. - Software: AstroImageJ (Collins et al. 2017), astropy (Astropy Collaboration et al. 2013, 2018), BANZAI (McCully et al. 2018), batman (Kreidberg 2015), BGLS (Mortier et al. 2015), celerite (Foreman-Mackey et al. 2017), emcee (Foreman-Mackey et al. 2013), exoplanet (Foreman-Mackey et al. 2019), PandExo (Batalha et al. 2017), PyMC3 (Salvatier et al. 2016), scipy (Virtanen et al. 2020), STARRY (Luger et al. 2019), Tapir (Jensen 2013), TERRA (Anglada-Escudé & Butler 2012).
Funding AgencyGrant Number
Hellman FellowshipUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
David and Lucile Packard FoundationUNSPECIFIED
John Templeton FoundationUNSPECIFIED
Agenzia Spaziale Italiana (ASI)2018-16-HH.0
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Japan Society for the Promotion of Science (JSPS)JP18H01265
Japan Society for the Promotion of Science (JSPS)JP18H05439
Japan Science and Technology AgencyJPMJPR1775
National Astronomical Observatory of JapanUNSPECIFIED
Gemini PartnershipUNSPECIFIED
Subject Keywords:Planetary system formation; Exoplanet structure; Radial velocity; Transit photometry; Low mass stars
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Planetary system formation (1257); Exoplanet structure (495); Radial velocity (1332); Transit photometry (1709); Low mass stars (2050)
Record Number:CaltechAUTHORS:20210813-181159077
Persistent URL:
Official Citation:Ryan Cloutier et al 2021 AJ 162 79
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110246
Deposited By: George Porter
Deposited On:16 Aug 2021 16:57
Last Modified:16 Aug 2021 16:57

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